Detergent compositions for washing fabrics conventionally contain a detergent active material and a builder material, the latter being added in order, inter alia, to reduce the level of free calcium ions in the wash liquor. While phosphate salts, particularly sodium tripolyphosphate, are often used as builder materials there is an increasing desire to use alternative materials in order to avoid any environmental problems which might arise due to the discharge of phosphate containing waste liquors into rivers and lakes. While a number of alternative builder materials have been suggested, water-soluble carbonates such as sodium carbonate are particularly attractive from the point of view of cost. However, the use of sodium carbonate as a builder material has certain disadvantages, amongst which are the tendency of the precipitated calcium carbonate to become deposited on the fabrics and the sensitivity of the calcium ion/carbonate reaction to poisoning by materials which may well be present, even unintentionally, in the wash liquors resulting in a final free calcium ion concentration which is not as low as is desirable to achieve good detergency.
While it might be supposed that the problem of deposition on fabrics could be overcome by the use of a colloid stabiliser it has been found that such materials are also carbonate precipitation crystal growth poisons and their use leads to a higher final free calcium ion concentration than is desirable.
It is known, for example from GB No. 1 437 950 (UNILEVER) to include high surface area insoluble carbonate material such as calcite in detergent compositions which include, for example, sodium carbonate as a builder, to act both as a seed crystal for the precipitating calcium carbonate and as an adsorbent for any crystal growth poisons which may be present. The use of a seed crystal ensures that the precipitated calcium grows to a crystal size which is sufficient that it will not be deposited on the fabrics. However, to be effective, calcite itself must be maintained in a dispersed state. In practice this has been difficult to achieve without poisoning the seed activity of crystalline forms of calcium carbonate.